Various methods of transmitting power wirelessly are known, including electromagnetic radiation. Such radiation is commonly used for wireless transmission of information, such as radio waves. Unfortunately, such transmissions are not an effective means for power transmission since the radiation disperses the energy in all directions.
One promising technology for transmitting wireless power is based on using coupled resonant objects. Two resonant objects of the same resonant frequency tend to exchange energy efficiently, while interacting weakly with extraneous off-resonant objects. An example of such a process is described in “Goodbye wires . . . ,” http://web.mit.edu/newsoffice/2007/wireless-0607.html, Franklin Hadley, Institute for Soldier Nanotechnologies, Jun. 7, 2007. In the described experiment, magnetically coupled resonators consisting of two copper coils (one for sending and one for receiving) are utilized to send and receive a non-radiative magnetic field that oscillates at a coupled MHz frequency. As noted, the advantage of using non-radiative fields is that most of the power not received by the receiving coils is bound to the vicinity of the sending unit, as opposed to being radiated into the environment.
Unfortunately, wireless power transmissions are limited to very short distances (e.g., a few meters). At present, there exist no practical implementations for delivering wireless power to a device that is moving about an expansive area.